Scotland Against Spin chairman, Graham Lang, said: “If the news is bad, bury it – which is why the census will not report until next year.”

Anti-windfarm campaigner Lyndsey Ward, from Kiltarlity, said protecting the population of the iconic golden eagles must be of “paramount importance”.

“Perhaps officials don’t want to know, or the public to know, what is really happening to the eagle population in Scotland so they can allow this turbine tsunami to continue unabated,” she said.

The RSPB said that while the population of golden eagles had been “static” for years, the cause was not windfarms but “ongoing illegal persecution”.

A Scottish Natural Heritage spokeswoman said that under a periodic review of the rolling programme of species surveys carried out by the Joint Nature Conservation Committee it was decided to move to a 12-year cycle.

This was partly to make sure that the rolling programme was affordable and to fit in with EU Bird Directive requirements for six and 12-year monitoring.

The spokeswoman added interim data suggested no decline in eagle numbers meant the census could be moved to a 12-year cycle, unlike hen harriers and capercaillie which were prioritised on a six-year cycle.